High-pressure fluid reservoirs, such as high-pressure fuel tanks, may use an isolation valve to open and close a vapor path between the fuel tank and a purge canister. In a typical evaporative emissions system, vented vapors from the fuel system are sent to a purge canister containing activated charcoal, which adsorbs fuel vapors. During certain engine operational modes, with the help of specifically designed control valves, the fuel vapors are adsorbed within the canister. Subsequently, during other engine operational modes, and with the help of additional control valves, fresh air is drawn through the canister, pulling the fuel vapor into the engine where it is burned.
For high-pressure fuel tank systems, an isolation valve may be used to isolate fuel tank emissions and prevent them from overloading the canister and vapor lines. The isolation valve itself may be a normally-closed, solenoid-operated valve that is opened to allow vapor to flow out of the tank for depressurization or any other event requiring a controlled vapor release.
Emissions systems may also include a fuel limit vent valve (FLVV) that vents the fuel tank during refueling until the tank is filled to a desired. When the tank is full, the FLVV closes, creating a pressure drop in a filler tube to initiate shutoff of a filler nozzle. The isolation valve may work in conjunction with the FLVV by limiting vapor flow rate to a level less than the maximum flow rate that the FLVV can handle. This prevents rushing fuel vapors from “corking” the FLVV to a closed position. The control provided by the isolation valve may also prevent corking of other vent valves (e.g., an over-pressure relief valve and/or a vacuum relief valve) in the emissions system.
The isolation valve and the FLVV, along with other vent valves, may be arranged in series with each other. However, there is a desire for a valve assembly that combines the isolation valve function with a venting function to provide a more efficient, compact assembly.